Increases the number of inventory slots from 12 to 14, then 16, and finally 18. If you plan on bringing along a lot of medikits and weapons, you may need the extra space. Note that your "toolbelt" increases by level, and only allows for seven additional slots, apart from your bare hands.

Increases the number of bullets picked up from ammunition drops (from enemies). A very handy skill to be coupled with Rain of Bullets. Maximizing this means you practically gorge Purna with ammunition each time she walks over an ammo pick-up.

Purna has a chance that she revives herself after being incapacitated. A handy skill, but maximizes at 30%. Consider two levels of this skill, so you have a one-in-five shot of being revived. Your only loss is money if you fail to revive ...

A great skill to have if you are looking for great (yellow-colored) weapons and items from metal chests. The chances are pretty slim, even if maximized (better than one-in-eight, or 15%). Consider maximizing or increasing this skill so you get great loot for your survivor party (remember that your character needs to be the one to open the chest, so Picklock may be a good complimentary skill).